1. Field of the Invention
The present invention relates to an axial force controlling method for controlling an axial force applied to a rolling bearing in a bearing apparatus having a shaft body, the rolling bearing being mounted to the shaft body such that the rolling bearing fits an outside of the shaft body, and the bearing apparatus.
2. Description of the Related Art
An unpublished axial force controlling method of the present inventors will be described by reference to FIGS. 5 to 7.
A bearing apparatus shown in FIG. 5 is a hub unit for a driving wheel of a vehicle. The hub unit has a hub wheel 10 as a shaft body and an angular ball bearing 12 which is mounted to a shaft portion 11 of the hub wheel 10 such that the ball bearing 12 fits an outside of the shaft portion 11 and which is an example of a rolling bearing of an inclined contact type. A free end of the shaft portion 11 is caused to bulge and deformed outward in a diameter direction by rolling caulking to form a caulked portion 13. The bearing 12 has an inner ring 12a, an outer ring 12b, a plurality of balls 12c, and two snap cages 12d. In the bearing 12, necessary preload is applied to the inner ring 12a by the caulked portion 13 and the bearing 12 is prevented from dropping off from the hub wheel 10.
Such a hub unit is mounted between a drive shaft 14 and a shaft case 15 of the vehicle. In other words, the shaft portion 11 of the hub wheel 10 is spline-fitted with the drive shaft 14 and connected to the drive shaft 14 by a nut 16 and an outer ring 12b of the bearing 12 is connected to the shaft case 15 by a bolt 17.
In the shaft portion 11 of the hub wheel 10, a caulking jig 20 as shown in FIG. 7 is held against a cylindrical portion 11a to be caulked on a free end side of the shaft portion 111 as shown by a phantom line in FIG. 6 before caulking. Then, by rolling the caulking jig 20 about a one-dot dashed line O at a constant angle a, the cylindrical portion 11a to be caulked is caused to bulge and deformed radially outward, thereby forming the caulked portion 13 held against an outer end face of the inner ring 12a. 
In the above bearing apparatus, because the caulked portion 13 is held against the outer end face of the inner ring 12a in order to bring the balls 12c into compressed states between the inner ring 12a and the outer ring 12b, a force for detaching the caulked portion 13 from the inner ring 12a in an axial direction acts on the caulked portion 13 on the contrary. As a result, an axially inward reaction force (hereafter defined as an axial force) for resisting the above force is generated from the caulked portion 13.
It is known that control for properly maintaining the axial force is necessary for ensuring a rolling property of the balls 12c. 
In the prior-art axial force controlling method, the axial force is controlled by merely caulking the caulked portion 13 firmly, adjusting a thickness of the caulked portion 13, or adjusting applied pressure in caulking. However, it is not easy to properly control the axial force by this method.
The present inventors have studied the axial force earnestly and as a result, found the following point. There is a caulking starting point on an inner periphery side of the cylindrical portion 11a to be caulked of the shaft portion 11 in caulking the cylindrical portion 11a on the outer end face of the inner ring 12a and outward in the radial direction by using the caulking jig 20.
When an end edge on the inner periphery side of a chamfered portion formed at an inner peripheral shoulder portion of the inner ring 12a was defined as a point A, the caulking starting point was defined as a point B, and a relationship between relative positions of both the points A and B was changed, it was found—that the axial force applied to the outer end face of the inner ring 12a from the caulked portion 13 varied.